1. Field of the Invention
The present invention relates to ultrasonic flowmeters, particularly, to an ultrasonic flowmeter for measuring the flow rate of a gas, a liquid, and the like by using an ultrasonic sensor.
2. Description of the Related Art
A conventional ultrasonic flowmeter 1 shown in FIG. 4 includes a fluid duct 2, and ultrasonic sensors 3 and 4 provided on the inner wall of the fluid duct 2. The ultrasonic sensors 3 and 4 are disposed opposing each other in a direction inclined by a predetermined angle with respect to a line perpendicular to the path of flow in the fluid duct 2. Each of the ultrasonic sensor 3 and 4 serves for generating and receiving ultrasonic waves.
In the thus configured ultrasonic flowmeter 1 shown in FIG. 4, the ultrasonic sensor 3 is located upstream and the ultrasonic sensor 4 is located downstream of a gas G which flows in the fluid duct 2 at a certain speed.
The ultrasonic sensors 3 and 4 simultaneously generate pulsed ultrasonic waves A and B, respectively, which are received by the ultrasonic sensors 4 and 3, respectively. In this case, time Ta taken for the ultrasonic wave A to be transmitted from the ultrasonic sensor 3 to the ultrasonic sensor 4 is shorter than time Tb taken for the ultrasonic wave B to be transmitted from the ultrasonic sensor 4 to the ultrasonic sensor 3, because the ultrasonic wave A follows the stream of the gas G while the ultrasonic wave B is against the stream. The difference between the times Ta and Tb is proportional to the speed of flow of the gas G.
Therefore, by detecting the difference between the times Ta and Tb, the speed of flow of the gas G can be measured, and when the cross-sectional area of the fluid duct 2 is known, the flow rate of the gas G can be measured with the speed of flow thereof.
A problem in the conventional ultrasonic flowmeter 1 is that a reduction in cost has not been possible because two ultrasonic sensors are required. Because of the two ultrasonic sensors being required, an additional controlling process is required so as to make the characteristics of the two ultrasonic sensors uniform, since the variation in characteristics between the two ultrasonic sensors deteriorates the measuring accuracy of the flowmeter. Another process is additionally required for selecting ultrasonic sensors having uniform characteristics, thereby preventing a reduction in cost.
Accordingly, it is an object of the present invention to provide an ultrasonic flowmeter in which a problem caused by variations in characteristics of ultrasonic sensors is solved, whereby a reduction in cost is possible.
To this end, according to an aspect of the present invention, an ultrasonic flowmeter comprises a fluid duct including therein first and second flow-paths separated by a partition and an ultrasonic sensor provided at one end of the fluid duct. A reflecting plate provided at the other end of the fluid duct reflects ultrasonic waves generated by the ultrasonic sensor and reaching the reflecting plate through the first and second flow-paths, and returns the ultrasonic waves to the ultrasonic sensor through the second and first flow-paths, respectively, which are different from the first and second flow-paths, respectively, through which the ultrasonic waves have reached the reflecting plate. First and second connecting flow-paths communicate with the first flow-path at the vicinity of one end and the other end, respectively, of the fluid duct.
The ultrasonic flowmeter according to the present invention may further comprise first and second connecting ducts connected with the fluid duct at the vicinity of one end and the other end, respectively, of the fluid duct. The first and second connecting ducts include the first and second flow-paths, respectively, formed in the first and second connecting ducts, respectively.
Manufacturing cost of the ultrasonic flowmeter thus configured according to the present invention can be reduced.